Information processing systems that include various apparatuses are presently in use. The apparatuses in such systems are interconnected via networks, predetermined cables, and the like so as to communicate with each other. TCP (Transmission Control Protocol)/IP (Internet Protocol) is one example of a protocol for transferring data in packets on a network.
The size of data and the amount of data to be transmitted in such a system can be reduced by compressing the communicated data. As one example, for a system where a personal computer and a printer can be connected via various types of communication interface, a method that selects whether to compress data transmitted to the printer has been proposed. According to this method, the personal computer decides whether to transmit compressed or uncompressed print data to the printer in accordance with the communication speed of a communication interface (i.e., data is compressed when low-speed communication is used). With this method, it would also be conceivable to compress the data to be transmitted, to acquire the compression ratio, and then decide whether to transmit the data compressed or uncompressed according to the communication speed of the communication interface and the compression ratio of the data.
See, for example, the following document: Japanese Laid-Open Patent Publication No. 2001-111432.
When managing system operations, it can be useful to have a communication monitoring apparatus collect and store the packets transferred between apparatuses. As one example, when a communication breakdown has occurred, the collected packets can be used to analyze the cause and/or what measures are to be taken. However, the amount of packets to be collected is huge and can easily exceed the capacity of a storage apparatus. It is possible to reduce the stored amount of data by compressing the collected packets, but this creates a further problem of the load of the compression processing.
As described above, the transmitted packets include both compressed and uncompressed packets. For packets that have already been compressed, further compression achieves little reduction in data size. The reduction in data size achieved by compression also varies from large to small depending on the type of data in the packets. Subjecting every packet, including packets for which compression achieves little reduction in size, to data compression increases the load of the compression processing and is inefficient. Also, if the load of the apparatus that collects packets increases, there is the risk that some packets may be dropped.